The invention relates to pump assemblies and pumping methods for diesel engines having Hydraulic Electronic Unit Injector (HEUI) fuel systems.
Diesel engines using HEUI fuel injectors are well known. A HEUI injector includes an actuation solenoid which, in response to a signal from the diesel engine electronic control module, opens a valve for an interval to permit high pressure engine oil supplied to the injector to extend a fuel plunger and inject fuel into the combustion chamber.
HEUI injectors are actuated by oil drawn from the sump of the diesel engine by the diesel engine oil pump and flowed to a high pressure pump assembly driven by the diesel engine. The pump assembly flows engine oil at high pressure into an oil manifold or compression chamber. The manifold or chamber is connected to the HEUI injectors. Except for large engines, the high pressure pump assembly typically includes a swash plate pump using axial pistons and having an output dependent upon the speed of the diesel engine. Large engines sometimes use a variable angle swash plate pump where the output can be varied independently of engine speed.
The pump assembly pumps oil at a rate depending on engine speed. The output must be sufficient to meet maximum flow requirements. The pressure of the oil in the oil manifold or chamber is controlled by an injection pressure regulator (IPR) valve in response to signals received from the electronic control module for the engine. The IPR valve limits the pressure in the pumped oil by flowing excess high pressure oil back into the engine sump.
A HEUI injection system uses an oil pump assembly to pump oil at a rate dependent upon the rotational speed of the diesel engine and independent of the actual instantaneous flow requirements for the engine and the temperature and viscosity of the engine oil. The pump operates at full capacity at all times, even when excess high pressure oil must be flowed or relieved back to the sump immediately to limit the pressure of the oil in the manifold as required by the engine electronic control module. Considerable power is required to drive the pump assembly at full capacity all the time. The energy required to pump high pressure oil which is relieved back to the sump is wasted and decreases the fuel efficiency of the diesel engine. Energy is converted to heat when high pressure oil is exhausted without doing useful work. The heat in the returned oil must be dissipated, typically by a heat exchanger. Heat exchanger capacity must be increased to accommodate the additional heat load.
There is a need for an improved high pressure pump assembly and method for use in a HEUI diesel engine to improve efficiency of the engine. When the engine oil is hot, the pump assembly should throttle low pressure oil supplied to the high pressure pump to maintain a desired instantaneous pressure in the manifold without over pumping and waste of energy. When the oil is cold, the engine oil pump should supply sufficient unthrottled oil to the high pressure pump for pumping to exceed the desired instantaneous pressure in the manifold. The energy required to pump excess high pressure oil should be used to speed warm up of the engine.
The invention is an improved HEUI pump assembly and method for a diesel engine. The pump assembly includes an inlet throttle valve for throttling the flow of oil supplied to a high pressure pump when the engine is warmed to a normal operating temperature. When the engine is cold the pump assembly flows unthrottled oil to the high pressure pump in a volume sufficient to meet or exceed pressure requirements. In a first embodiment this is done by an inlet throttle valve deactivator maintaining the inlet throttle valve fully open when the engine is cold. With the inlet throttle valve held open, unthrottled cold oil is supplied through the valve to the high pressure pump, the pump maintains the desired instantaneous pressure in the manifold and the engine is drivable. In a second embodiment, when the engine is cold a normally closed passage extending from the output of the engine oil pump to the inlet of the high pressure pump is opened to bypass the inlet throttle valve and supply unthrottled cold oil directly to the high pressure pump. The high pressure pump provides a high pressure output sufficient to maintain the desired instantaneous pressure in the manifold and make the engine drivable. In both embodiments, the volume of pumped cold oil may exceed the volume of oil required to maintain the desired instantaneous pressure in the manifold and fire the injectors. Excess pumped cold oil is relieved back to the sump. The pressure energy released from the relieved oil is converted to heat energy to speed warming of the oil and engine.
Once the engine oil reaches a desired temperature the pump assembly automatically activates the inlet throttle valve for normal operation. In the first embodiment, the inlet throttle valve is freed for valving movement. In the second embodiment, the bypass passage is closed. In both embodiments, the inlet throttle valve throttles the oil flowed to the high pressure pump to meet the instantaneous pressure requirements of the engine without substantial over pumping. Throttling of oil supplied to the pump increases the efficiency of the engine by reducing the power required to operate the pump when the required instantaneous flow is lower than pump capacity.
The temperature for the engine oil when the inlet throttle valve is activated may be higher than the lowest oil temperature at which the inlet throttle valve works properly. A higher activation temperature may be selected to reduce the time to warm up the engine to a temperature sufficiently high to reduce combustion emissions.
Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawings illustrating the invention.